1. Field of the Invention
The present invention relates to a polarized electromagnetic relay. The present invention also relates to a coil assembly adapted to be used in a polarized electromagnetic relay.
2. Description of the Related Art
A polar or polarized electromagnetic relay, wherein an electromagnet assembly including an electromagnet and a permanent magnet as well as a contact section including a plurality of contact members are insulated from each other and attached to a base, and wherein a force transfer member shiftable under an action of the electromagnet assembly to make the contact members of the contact section open or close is disposed between the electromagnet assembly and the contact section, has been known in the art. For example, Japanese Unexamined Patent Publication (Kokai) No. 58-181227 (JP-A-58-181227) discloses a polarized electromagnetic relay of this type, in which an electromagnet assembly is configured so that a magnetic movable element (referred to as “an armature section” in JP-A-58-181227) including a permanent magnet and a pair of yokes or iron plates, holding the permanent magnet therebetween, linearly shifts in a direction parallel with a center axis of a coil in response to the excitation of the electromagnet. Typically, the electromagnet assembly configured as described above has an advantage that outside dimensions can be effectively reduced in a redial direction of the coil of the electromagnetic relay, in comparison with a configuration in which a magnetic movable element including a permanent magnet linearly shifts in a direction orthogonal to the coil center axis in response to the excitation of an electromagnet.
In the polarized electromagnetic relay disclosed in JP-A-58-181227, two large and small U-shaped yokes are assembled together to hold, between the center areas of the yokes, a permanent magnet in a direction of magnetization of the magnet, so that at longitudinally opposite end regions of the magnetic movable element, end portions of the yokes, on which respective magnetic poles are formed by the magnet, are arranged so as to face to each other. Similarly, an iron core of the electromagnet is a U-shaped member, of which longitudinally opposite ends extend in a radial direction of the coil and protrude outward. At each longitudinal end region of the magnetic movable element, each end portion of the iron core of the electromagnet is inserted into a space between the end portions of a pair of yokes, at which mutually different magnetic poles are formed. The magnetic movable element is integrally incorporated in a force transfer member as a molded component, and when the electromagnet operates under the above described relative disposition, the force transfer member linearly shifts together with the magnetic movable elements, so as to make the contact section open or close.
Further, a polarized electromagnetic relay, wherein an electromagnet includes a bobbin, on which a conductive wire is wound to form a coil, and at least three coil terminals securely supported on the bobbin, the wire of the coil being connected to each of the coil terminals (see, e.g., Japanese Unexamined Patent Publication (Kokai) No. 2005-243367 (JP-A-2005-243367)). In this type of the polarized electromagnetic relay, the coil may constitutes two excitation circuits, each of which includes a terminal pair defined by any two coil terminals of the at least three coil terminals, and thereby an advantage is given, such that an operation mode of the relay can be quickly switched between an operating state (i.e., a make-contact closing state) and a reset state (i.e., a break-contact closing state), and in either state, the contact section can be stably kept in the contact closing state.
In the polarized electromagnetic relay disclosed in JP-A-58-181227, the pair of U-shaped yokes constituting the magnetic movable element have lengths substantially corresponding to an entire length of the U-shaped iron core of the electromagnet, so that the dimension and weight of a movable section including the force transfer member are relatively large, which may influence the response (i.e., operating time) and outside dimensions of the relay. Further, in this configuration, the U-shaped iron core of the electromagnet and the U-shaped yokes of the magnetic movable element cooperate with each other by simultaneously exerting magnetic effects at their longitudinally opposite ends, so that in order to reduce unevenness of operational characteristics, it is necessary to improve the dimensional accuracy of these components, which may increase manufacturing costs.
On the other hand, in the polarized electromagnetic relay in which the electromagnet includes at least three coil terminals as described in JP-A-2005-243367, it is required to safely and accurately perform an automatic winding process for connecting the conductive wire to each coil terminal and thereby forming the coil on the bobbin.